Exciter system for thyratron power inverters and the like



April G. W. DEMUTH EXCITER SYSTEM FOR THYRATRON POWER INVERTERS AND THE LIKE INVENTOR EALAN W. DEMu'n-I Ww/f @www ATTORNEYS` April 17, 1951 G. w. DEMUTH EXCITER SYSTEM FOR THYRATRON POWER INVERTERS AND Tm: LIKE 2 Sheets-Sheet 2 Filed Sept. 13, 1949 Y ,m M AJMWM -Mwwwwmg J m Nlw mk n m E m NQ. vg D m WM n m W m @a m .wv n L, \w\\\\%-.k\\ n knm. knu A .QN mw" @W Patented Apr. 17, 1951 EXCITER SYSTEM FOR THYRATRON POWER INVERTERS AND THE LIKE Y Galan W. Demuth, Moorestown, N. J., assignorto Bryant Chucking Grinder Company, Springfield, Vt., a corporation of Vermont Application September 13, 1949, Serial No. 115,526

22 Claims.

The present invention relates to frequency control or exciter systems for thyratron power inverters and the like, and has for its primary object, to provide an improved frequency control or exciter system for operation of thyratron inverters and the like at relatively high frequencies with maximum eiciency.

It is also a further and :more specific object of the present invention, to provide an electronic two-phase high frequency triggering pulse generator system for the control of thyratron power inverters and the like, in alternating current variable speed industrial motor applications.

A variable frequency power supply system for the speed control of alternating current industrial electric motors and the like, of the type to which the present invention is particularly related, is shown, described and claimed in a copending application of Willis F'. Moore, Serial No. 57,237, filed October 29, 1948, for Variable- VFrequency Power-Supply System, and assigned to the same assignee as this application.

In the system referred to, a variable-frequency oscillator is coupled to a full-wave grid-controlled gaseous discharge tube or thyratron power inverter for triggering the inverter at the oscillator frequency and providing alternating current power therethrough for high-speed induction motors adapted for directly driving tool elements in high-speed grinding, woodworking, and other industrial operations. By varying the operating frequency of the Oscillator and thereby the rate of triggering of the thyratrons through special circuit means, the speed of the motor is varied or adjusted as desired. This electronic variable-frequency power supply system thus provides improved means for deriving and controlling high frequency alternating current power for the operation of high-speed industrial motors.

It is also an object of the present invention to provide an improved high frequency exciter or control system for thyratron power inverters and the like, which is adapted for two-phase or other polyphase operation, and for the production and application to thyratron inverters of variable frequency triggering pulse waves of predetermined polarity and amplitude, whereby more efcient operation of thyratron inverters in high-speed motor control systems and the like may be attained.

It is also a further object of the present invention to provide a high frequency triggering pulse generator or exciter system for polyphase thyratron power inverters and the like, whereby a plurality of full-wave thyratron inverter power control circuits m-ay be operated simultaneously thereby for the production of polyphase alternating current power, for high speed industrial motors and the like. I

In an alternating current power supply system for operation at relatively high frequencies, for example in a range of audio frequencies of from flve hundred cycles to two thousand cycles and higher, the deionizing time of the thyratronsand the constants of the circuits for both lpower output and triggering must be carefully coordinated to provide effective power output. In particular, the sine-wave source of triggering potential, and the modification of the sine wave to provide a corresponding peaked pulse wave, are important for the proper excitation of the thyratrons for the production of highA frequency alternating'current power in such systems.

It is, therefore, a further and important object of this invention, to provide a sine-'wave-based, triggering-pulse wave exciter system for one or more thyratron power inverters with full wave output in a high frequency power supply circuit. It is likewise an object of the invention, to provide such an excitation system that is adapted for unitary self-contained construction, and which may be applied to the single phase operation of a single pair of thyratrons.

In accordance with .the invention, a tunable oscillator is provided with amplitude Yand feed'- back stabilizing and low-pass filter circuits, whereby a substantially smooth sine-wave output may be obtained with substantially`v constant amplitude and, when desired, with Variable-frequency control over a predetermined, relatively wide frequency range within the limits above re'- ferred to. The oscillator is suitably coupled to a phase-shift network and voltage equalizer circuit, whereby a two-phase or polyphase variable frequency output voltage may be obtained from the oscillator, for polyphase excitation of high frequency inverters.

The operation of the system in accordance with the invention, is such that the input alternating current signal voltage for each phase'is substantially a sine wave of-practically constant amplitude for all frequencies within the range "of operating frequencies desired, and is substantially symmetrical. The signal voltage in each phaseis thereafter applied to suitable phase inverter stages, which provide for push-pull operation in each phase for triggering or excitation of the full- -wave thyratroninverter stages whichV follow in the power control circuit. Between the phase in'- verter section of the'variable frequency control system and the utilization or thyratron circuit, a wave-Shaper circuit with push-pull input is introduced in each phase or amplifying channel for transforming the smooth sine wave into spaced, substantially sharp voltage pulses of predetermined polarity and amplitude, and the final output potential in each phase or channel is directly coupled to the utilization circuit or thyratron stage through suitable coupling circuits or networks whereby the pulse wave shape is maintained.

The oscillator is adapted for operation over a relatively wide frequency range in a series of steps, being variable therebetween or xed, as desired for any particular application. A variable frequency control system in accordance with the present invention is particularly adapted for the production of two-phase push-pull alternating current triggering or excitation voltages of variable frequency, and the system, furthermore, is adapted for unitary assembly on a single chassis or supporting structure for application to existing apparatus of the type referred to, as a control unit, and is therefore provided with its own plate or power supply circuit. The system also involves theV use of a plurality of electronic oscillator and amplifier tubes, many of which may be dual triodes for simplicity of construction. The whole unit is adapted for plug-in connection with the remainder of the power supply system for which it is the controlling element, as will hereinafter be seen.

In its application to a two-phase power supply system adapted, for example, to the operation of a two-phase high-speed motor, or other polyphase power circuits, an embodiment of the invention may include an electronic oscillator which provides a two-phase output voltage by means of a resistance-capacitance or a resistance-inductance voltage divider system. The wave form of the oscillator voltage is rendered sinusoidal through the use of the low pass filter which removes harmonics above the highest desired frequency, for example above 1700 cycles, in order to enable proper phase division with either of the divider systems referred to, and is suitably limited in amplitude.

The two-phase control voltage thus generated and derived may subsequently be applied to push-pull amplier stages through phase inverter means, resulting in a push-pull sine wave of large amplitude in each of the two phases. The final amplifier stages for each phase are suitably controlled and biased so that the sinusoidal wave causes a plate current to flow for less than half of one cycle. The output wave form for each of the two phases is thus given a pulse shape suitable for controlling a thyratron power circuit for full-wave operation with maximum eiiiciency. The same arrangement may also be provided for other polyphase circuits in which the sinusoidal wave is subsequently modified to the pulse shape.

Another feature of the invention is involved in the special equalizing amplifier for one phase of the two-phase system, which automatically regulates the signal voltage to equal the amplitude of the signal voltage of the other phase at all adjustments of the frequency. This is for the reason that, for example, in the two-branch resistance-capacitance voltage divider system which produces the two output voltage components, the lagging phase follows the original voltage wave by ninety degrees, and tends to vary Widely in amplitude with frequency change, be-

ing referred to hereinafter as phase B. The other or direct voltage component is relatively constant, and is referred to hereinafter as phase A.

Accordingly, it will be seen that it is an object of this invention to provide an improved electronic high-frequency system for producing a two-phase voltage for thyratron excitation or control, and thereby for more effectively and eiliciently controlling the operation of high-speed motors for industrial applications, particularly in the eld of high-speed internal grinding, where the tool speeds may reach values as high as 100,000 R. P. M. and higher. For such work, high-speed two-pole squirrel cage induction motors are provided, having relatively small rotors directly connected with the grinding wheel tool.

With such motors, it will be seen that, for a speed of approximately 36,000 R. P. M., a supply of 600 cycles per second may be provided, whereas for higher speeds, such as aproximately 180,- 000 R. P. M., for example, a supply frequency of 3,000 cycles per second may be provided. It is to such range of frequencies that the high frequency exciter or control system of the present invention is particularly adapted.

It is likewise an object of this invention, to provide an improved variable frequency exciter or control system for generating two-phase excitation voltages for the full-wave operation of a thyratron inverter or a plurality of inverters, which is readily adjustable over a wide frequency range without variation in the output voltage of either phase, and which operates to maintain an output wave form for each of the two phases which is of a pulse shape and polarity suitable for controlling the thyratron circuit with maximum eiiiciency.

While the polarity of the pulse wave applied to a thyratron inverter of the push-pull type may include positive and negative alternate pulses corresponding to the alternations of the initial sine wave, for extremely high frequency opera-r tion of vthe thyratron inverters in the range of frequencies referred to hereinbefore, including. for example, frequencies of from 1700 to 2000 cycles and higher, as are required for high speed induction motor operation, the steady state negative bias on the thyratrons is, according to the invention, maintained near the limit of the normal tube rating to obtain a more rapid deionization time. Under such conditions of operation, no negative pulses can be tolerated on the open tube without risking tube breakdown between the control grid and other electrodes.

Therefore, it is a further and important obiect of this invention, to provide an improved high frequency exciter system for thyratron inverters which operates to produce positive triggering pulses of predetermined amplitude, duration and shape, while suppressing the corresponding negative half-wave pulses. Such a system, in accordance with the invention, permits the maximum negative bias on each thyratron inverter stage for producing eifective or full deionization even at the highest frequency, and requires a relatively high degree of amplification or pulse amplitude for proper triggering action.

Protective series resistance means in the thyratron grid circuits prevent the application of positive grid voltages higher than a relatively low normal value, as the thyratrons presently used are designed to fire at relatively low voltages. In the design of the exciter system, the gain from the oscillator through the system, to the thyratron grids, is adjusted so that at substantially all frequencies, the pulse peaks are of such magnitude as to overcome the negative bias and to provide the positive voltage limit indicated. In the case of over-excitation, the series grid resistors serve to maintain the voltage on the grids at the upper limit.

The novel features that are considered to be characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to a specific organization and a preferred method of operation, as well as additional objects and advantages thereof, will further be understood from the following description when read in connection with the accompanying drawings, in which:

Figure 1 is a schematic block diagram of a frequency control or exciter system for thyratron power inverters and the like, embodying the invention;

Figure 2 is a schematic circuit diagram of the frequency control or exciter system shown in Figure 1, showing the details of a preferred embodiment of the invention as applied to the triggering of a full-wave, two-phase thyratron inverter in a high frequency power supply system; and

Figure 3 is a schematic circuit diagram of a portion of the circuit of Figure 2, showing a modification of the invention.

Referring to Figure l, the invention is shown in its application to the control of a two-phase, high-speed motor 5, which is directly connected to drive a high-speed tool 6, such as a grinding wheel, which may operate in a speed range of the order of from 3,000 to 100,000 R. P. M.

The motor receives power from a pair of fullwave thyratron inverters 'I and 8, which are coupled, respectively, with two-phase input leads 9 and I0 through suitable output coupling networks I land I2. For the operation of the motor at the speeds referred to, a frequency of from 500 to 1700 cycles is applied to the full-wave thyratron inverters 1 and B from a variable frequency sine-wave oscillator I5, having a variable frequency control network I by which the frequency is adjusted for the desired motor speed; that is, for the excitation or triggering of the fullwave thyratron inverters, through manipulation of controls TI and '18.

An amplitude limiter circuit I1 is arranged in connection with the oscillator for preventing excessive voltage generation at the high frequency end of the frequency control range of operation of the oscillator, and a feedback stabilizer circuit, indicated at I8, is connected with the oscillator for maintaining the feedback at a relatively low value at all frequencies, thereby to provide an approximate sine-wave shape with a minimum of distortion.

A low pass filter and amplifier 2B is arranged to receive the output from the oscillator and to pass the highest operating frequency, which in the present example is 1700 cycles. B-y this means, any harmonics which normally would be amplified and passed on to the phase-shift network are suppressed, so that only a pure sine wave at the desired frequency is derived from the oscillator. This circuit may also be adapted for amplifying the output voltage derived, so that it is restored to its original value after passing .through the filter.

A resistance-capacitance two-branch voltage divider or phase-shift network 2| is arranged to receive the output of the low pass lter and to divide the sinusoidal output voltage into two separate and corresponding voltages or voltage components, one of which lags in phase from the original voltage by degrees. This is applied to a voltage equalizer amplifier 22, while the other leading or in-phase component is applied directly to a phase-inverter means or amplifier stage 23. Since the voltage applied to the voltage equalizer 22 from the lagging phase varies widely in amplitude with frequency change, the equalizer includes gain control means whereby the lagging voltage component is automatically regulated to equal the amplitude of the leading phase at all adjustments of the frequency. The output voltage is then applied to a second phase-inverter means or amplifier stage 24 in a separate control channel.

The phase-shift network 2l and voltage equalizer amplifier 22 serve to provide, at the phase inverter stages 23 and 24, a two-phase voltage, that is, two sine-wave voltages, 90 degrees out of phase, which are substantially equal in both phases. As indicated, the phase inverter stages 23 and 24 are the initial stages, respectively, of the two-phase branches or control channels, and may be referred to as phase A and phase B, as hereinbefore noted.

The two-phase voltages derived from the phase-inverter stages 23 and 24 are balanced or push-pull voltages in each phase and are of sufcient amplitude for operating the following pushepull wave-Shaper amplifier stages 25 and 26, respectively. These amplifiers are provided by suitable electronic tube means, so biased that the balanced sinusoidal input wave on each stage produces a balanced output wave-form for each of the two phases that is of a predetermined pulse shape, each pulse being less than one-half cycle in width or durationand of suitable amplitudey for effectively controlling a thyratron power circuit or thyratron inverter of the type indicated at 'l and 8 for motor control purposes. In order to preserve the pulse shape and properly to apply the pulses to the full-wave thyratron inverters 1 and 8, a push-pull impedance coupling network is provided between each push-pull wave shaper amplifier and the following full-wave thyratron inverter, as indicated at 21 and 28.

In the high frequency control system shown, the frequency of the sine-wave output signal from the oscillator may be varied or adjusted by means of the frequency control network. The output signal at the established frequency is passed through the low pass filter and amplifier 20, thence through the ,phase-shift network 2| to the phase-inverter stage '23 directly in the phase A channel, and through the voltage equalizer 22 to the phase inverter stage 24 in the phase B channel.

The sine-wave output signal is then applied in push-pull through the inverter stages 23 and 24 to the push-pull wave-Shaper amplifiers 25 and 26, and thence through the coupling networks 21 and 28 to. the triggering circuits of the full-wave thyratron inverters 'I and 8, thereby controlling the power output to the two-phase motor 5 through the two-phase output coupling networks II and I2. The high speed tool 6 then operates at the selected speed as determined by the frequency setting of the oscillator frequency control network I6, and the adjustment of the output coupling networks I I and I2 through the coupling connection 8B with the control knob TI.

A more comprehensive study of the system is provided by reference to Figure 2, along with Figure 1, in which the complete circuit details of the system of Figure 1 are shown.

Referring now to Figure 2, along with Figure 1, in which like elements are designated throughout by the same reference characters, the oscillator l5 comprises an electronic oscillator tube 30, which may be one triode section of a suitable SSN? double triode. An LC tank circuit is used in a Hartley type of oscillator, comprising a main inductance having a grid section 3l, an anode section 32, and a frequency control network i6 connected therewith through leads 33 and 34, the latter being connected to the ground lead 35 for the system.

One terminal 36 of the inductance 3l--32 is connected to the ground lead 35, while the opposite high potential terminal 31' is connected with the lead 33, and with a lead. 38 terminating in the anodes 39 of a rectifier tube iii) in the amplitude limiter circuit l1. The lead 38 is also coupled to the control grid 45 of the oscillator through a grid capacitor 4i and a grid-leak resistor 42 of relatively low resistance value. The latter is connected to the cathode tap 43 on the tuned induotance 3|-32, along with the cathode 44, in circuit with which is provided a cathode resistor 45 for applying degeneration to the oscillator for smoothing the operation thereof, and helping to eliminate any tendency to block.

The oscillator anode 4T is connected through a feedback stabilizing circuit, comprising a series resistor 48 and a series capacitor 49, with the terminal 36 and ground. Oscillator anode potential is supplied from a positive anode supply lead 5d through a coupling resistor 5i. The resistor 48 in the anode circuit connection with the inductance 3 l-32, by way of the capacitor 49 and the terminal 36, serves as a stabilizer to maintain the feedback at a predetermined relatively low level and permits the oscillator to operate over a wide frequency range without blocking at either end of the range. The bias or cathode resistor 45, also effectively in circuit with the anode, provides a biasing potential which also aids in stabilizing the operation of the oscillator at all frequencies, and with the feedback stabilizer tends to produce a smooth sine-wave voltage output which has been found to be desirable as a base for two-phase or other polyphase signal generation.

The oscillator signal output voltage is taken from a terminal 43 or cathode connection on the oscillator, or tuning inductance, through the low pass ilter 20. A coupling capacitor 52 is connected serially between the terminal 43 and the filter which comprises a limiting resistor 53 and a tapped resistor 54 in series to ground, with a shunt capacitor 55 connected with the resistor 54. A tap connection 59 on the resistor 54 serves to determine the oscillator output potential to be applied through an output lead 56 to the control grid 5? of a buffer amplifier electronic tube 58, and is adjusted to give the optimum range of operating voltages to the voltage equalizer amplifier 22 and a control grid therein. The gain of the amplier tube 58 serves to restore the voltage loss in the low pass filter at certain frequencies. Like the oscillator and other tubes, it may be provided by one section of a standard commercial GSNT tube.

The oscillator peak voltages are limited in amplitude by means of the limiter circuit l1. This includes a rectifier tube 40 and a series resistor 6l connected in the cathode circuit 52 of the 8 rectifier, and is completed through a capacitor 63 to the ground lead 35 and the terminal 36 of the oscillator tank circuit. Thus the rectifier 40, the resistor 5I and the capacitor t3 are serially connected across the oscillator tank circuit between the terminals 36 and 3i.

The damping or limiting action of the resistor 6i on the circuit is adjusted for the same amplitude of oscillations at the high frequency end of the range as at the lo-w frequency end, by adjusting the positive bias on the rectifier cathodes through connection of the cathode circuit lead 62 with an adjustable contact 65 on a bleeder resistor 65, which is connected in a voltage bleeder circuit between the high positive anode supply lead 50 and ground 35. A series voltage dropping resistor 61 is provided to limit the Voltage adjustment range of the contact element 65-56, which regulates the positive bias on the cathode circuit of the rectifier 45. When the established bias voltage is exceeded, the rectifier breaks down and applies the resistor 6I across the tank circuit, limiting the high amplitude peaks which may occur in operation, particularly at the high frequency end of the tuning range.

The frequency of the oscillator is variable by means of a four-gang variable capacitor comprising elements 'l0- '13 inclusive, provided with suitable trimmer capacitors i4 and series track ing capacitors f5, and further being selectively connectable in circuit through a four-step tap switch 16. The tap switch is operated by a control knob indicated at il, while the four-gang capacitor is operable by a second variable control knob '.f, providing, respectively, frequency range and variable frequency control of the oscillator. As will be seen from an inspection of the circuit connections, the four-step, three-pole tap switch 'i6 provides for successively and selectively connecting the capacitors I0-13 in circuit across the main inductance 3|-32, between the leads 33 and 34.

The four-step frequency range control for the oscillator is representative of any suitable number of frequency ranges to be selected for any given installation or operation. In the present example, for the operation of high-speed grinding tool motors within the speed ranges hereinbefore referred to, the four steps provided in connection with the switch T6 may be considered to provide the following frequency ranges, each of which is variable by means of the control knob 18 between the limits indicated:

Frequency R. P. M. Step Speed in C. P. S. (Synchronous) High l, 3D0-1, 700 78, OOO-102, U00 Intermediate 1, OOO-1, 300 60. 00078, 000 ledlllm 70D-1, 00D 42. 000-60, 000 LOW. l 50G-700 30, OOO-42, 000

This provides a range of speed from 30,000 R. P. M. to 102,000 R. P. M. for a two-pole induction motor, when connected with a suitable thyratron power supply system.

It will be noted that the frequency range control means may provide for adjustment of other portions of the power supply system in certain cases, as indicated by the dotted line connection 80 leading Vto the inverter output circuits. For example, as indicated by the legend, this connection may serve to control means whereby the thyratron inverter stages 'i and. 8 are conditioned for operation in each of the various frequency ranges with maximum eiiiciency. An

arrangement of controls for this purpose may include` a thyratron commutation or quenching control as may be desirable for wide frequency range of operation. However, this connection may be used for other purposes, for adjusting various circuit means in connection with the speed range control, and as the specific connection to other portions of the system, except as above, does not concern the present invention, further description is believed to be unnecessary.

The four-step range control for the oscillator frequency is representative of any desired number of frequency steps which may be provided for the sine-wave oscillator, and likewise the overall frequency range may be modified or extended, or the frequency may be fixed at one or more predetermined values in accordance with .the requirements for any particular frequency supply for control purposes. However, the present four-step speed range control is shown for the reason that it is particularly well adapted for the excitation of thyratron inverters for'variable speed alternating current industrial motors for high-speed operation.

The four-gang variable frequency control system, comprising the capacitor sections -13 and the tracking capacitor network in connection therewith, also represents a present preferred arrangement for speed variation through each speed range, although other suitable means may be provided, and in some instances the variable speed feature may be eliminated where the motor speed, for example, is to be adjusted in successive predetermined steps only, or xed at one speed.

While a stabilizing Hartley type oscillator, as shown, is presently preferred, any suitable LC type stabilized tuning system, or any other stable sine-wave source, may 4be utilized. Likewise,

-oscillation peak limiting is desirable as provided by the Series rectier and resistor peak limiter circuit across the main oscillator tuning inductance, in the present example, with threshold adjustment for the operation of the rectifier. This circuit operates to preserve the wave form at high frequencies in that the oscillator peak voltages are suppressed thereby, and the feedback stabilizer circuit, comprising the series resistor 48 and the capacitor 49 in the anode return circuit to the oscillator tuning -inductance, serves to preserve the sine-wave output form of the signal voltage delivered by the oscillator at all frequencies. It will be noted that this feedback stabilizer circuit is not in the main LC circuit of the oscillator, and thus serves to control the feedback to a suflicient value to maintain the oscillations at all frequencies within the desired operating range without interfering with frequency adjustment of the control network.

To further preserve the wave shape and to prevent harmonics from being delivered to the output circuit of the oscillator and to the phasedivider` network in accordance with the inven- `by aids in attaining a balanced voltage output through the phase shift network which follows the buffer amplier in the output circuit of the Oscillator.

Thephase shift network comprises two circuits or branches connected in parallel across the buffer amplier output circuit comprising an anode lead 82 and the ground lead 35. One branch of the circuit comprises a resistor 83 and a capacitor 84, in series, in the order named, from the lead 82 to the ground lead 35, whereas the second branch includes a capacitor 85 anda resistor 86, also in the order named, between the leads 82 and ground 35. An output tap connection 31 between the resistor 83 and the capacitor 84, and a second out-- put tap connection B8 effectively between the capacitor 85 and resistor 8B, provide a two-phase output connection for the oscillator. The tap connection 88 is in the 'form of a potentiometer contact operative in connection with the resistor. 86, which is a potentiometer resistor. The values of the capacitors 84 and 85 are the same and equal,

and may be considered to be of the order of .1

mfd., while the resistors 83 and 86 are likewise equal, and each may likewisev be of the order of 100,000 ohms in the present example.

The oscillator output voltage is applied to the two parallel resistance-capacitance voltage dividers above described, through the circuit 82-35 across the anode coupling resistor 89, which is connected with the anode lead 82 and a filter resistor 90 in the positive anode supply lead 50.

The filter resistor is provided with a suitable bypass capacitor to ground, indicated at 9|.

The in-phase or leading phase voltage, which may be referred to as the phase A voltage, is derived from the potentiometer contact or output tap connection 88, while the out-of-phase or lagging phase voltage derived from the terminal or output tap connection 81 at the junction of the resistor 83 and the capacitor 84, being the phase B voltage, lags 90 degrees in phase from phase A. This 90-degree phase difference is the result of using identical resistance and capacity values in the two parallel resistance-capacitance dividers in reverse order, as described. Thus, the alternating currents through the two divider circuits are identical, both in phase and magnitude, for all frequencies of operation, so that the alternating current output voltage across the capacitor 84 inherently differs in phase by 90 degrees from the corresponding output voltage across the resistance of the potentiometer 8B.

Broadly, this result is obtained for any parallel set of dividers having the same ratios of resistance to reactance. However, identical values of resistance and capacitance seem most practical.

The magnitude of the phase B voltage at the voutput terminal 81 varies substantially inversely eliminate the complications of manually adjust- `ing the phase B voltage to equal the phase A voltage for different oscillator frequency adjustments, and automatically to equalize phase A and phase B voltages during changing oscillator frequency or speed change adjustments, an equalizer circuit is provided for the output circuit of the oscillator, and is located in the phase B- branch of the phase shift network. f

The equalizer circuit comprises a variable gain amplifier stage including an electronic amplifier tube 93, to the control grid 94 of which output signals from the phase B terminal 81 of the phase shift network are applied through an output lead 95 and a coupling capacitor 96. The grid 94 is provided with a grid resistor connection 91 with the ground lead 35, and the cathode 98 ofthe amplifier tube 93 is connected likewise to ground,

i1 through a self-bias resistor 99 provided with a suitable bypass capacitor |00. Thus the grid 94 is self-biased.

The rtube 93 is provided with a screen grid |02, which is energized through a filter network from the positive anode potential supply lead 50 comprising a series of voltage bleeder resistors |03- |01 inclusive, with an intermediate tap connection at |08 for the coupling resistor |33 for the grid 02. Thus the screen grid is providedv with a nor- L malV positive potential which is substantially lower than the potential at the lead 50 by the amount of the drop in the bleeder resistor sections |03 and |04. A bypass capacitor is provided for the first bleeder resistor section |03, and likewise the 'screen grid |02 is bypassed to ground through a suitable bypass capacitor The, amplifier tube 93 is provided with a suppressor grid ||5, to which is applied a variable kgain controlling potential responsive to the applied signal wave and derived through a signal r'ectier tube ||6 and a signal amplifier tube ||1 "coupled through a coupling capacitor i8 with the 'oscillator signals applied thereto through phase B.

The rectifier HE is coupled to the amplifier tube through an output coupling network comprising an anode or plate resistor in the anode circuit |22 of the tube ||1 and a coupling capacitor |2| through which signals are applied to the anodes |23 of the rectifier H6.

The rectifier is provided with an output circuit lead |24 connected between the rectifier anodes |23 and the cathode 98 of the variable gain control amplier `93, through a series potentiometer resistor |25. The suppressor grid ||5 of the tube 93 is connected to an adjustable tap |26 on the potentiometer resistor |25 through a coupling resistor |21, and the grid ||5 is suitably bypassed to ground through a bypass capacitor |28. `The cathodes |29 of the rectifier H6 are likewise connected in parallel and to an `adjustable contact |30 on a potentiometer resistor |06.

to ground through a grid coupling resistor |33,

and is suitably biased through a cathode resistor |34. Any suitable electronic amplifier may be utilized to provide amplified signals for the rectifier H6, which likewise may be provided by other suitable means than the double diode shown.

Thus the control grids of the gain controlling stage 93 and of the amplifier tube ||1 are connected in parallel to the phase B output voltage source 81. The tube 83 is of the pentode type, provided, for example, by a commercial tube known as type 6AS6, the suppressor grid of which provides the gain control element. The tube |11 is likewise of the pentode type, such as a commercial type known as 6AU6, but is operated as a triode amplifier for amplifying the phase B voltage for subsequent rectification by the rectifier IIB.

With the present arrangement, the potentiometer resistor |25 is effectively connected in shunt across the rectifier IIS, and in response to signals through the amplifier ||1 and the rectifier ||6, it will be seen that an increasing negative bias will be applied to the suppressor grid ||5 as the signal amplitude increases, this potential being with respect to the cathode 98. The cathode 98 may be at any predetermined positive potential with respect to ground as determined by the cathode resistor 99. It is for this reason that the potentiometer resistor |25 and the rectifier output circuit therethrough is connected directly to the cathode 88, so that the bias on the grid ||5 is always independent on the bias on the control grid and the drop in the cathode resistor 59. The negative bias voltage produced by the rectifier ||`6 is applied to the suppressor grid H5, through the potentiometer |25 and the resistor |21, and the capacitor |23 acting as a filter.

The potentiometer contact |30 is so adjusted that a threshold bias is applied to the rectifier H5, whereby it starts to rectify when the signal potential in the output circuit 95 attains a predetermined minimum value, as at the high frequency end of the tuning range of the oscillator. As the frequency of the oscillator is decreased in operation, in controlling the speed of the motor or other utilization means connected with the system, it will be seen that the voltage across the phase shift network capacitor 84 will increase as the impedance of the capacitor increases with decrease in frequency, thereby applying a higher signal potential to the amplifier ||1 and the rectifier H5, and resulting in an increasing negative bias across the potentiometer |25 after the initial or threshold bias on the rectifier is overcome. This, in turn, increases the biasing potential on the grid ||5 and tends to reduce the gain of the amplifier 93 accordingly in proportion, thereby to maintain the signal output therefrom substantially constant in amplitude.

After initial adjustment, the gain of the amplifier 33 is caused to vary inversely with the amplitudepf the phase B voltage, so that the output of' the tube 93 produces substantially a uniform voltage level which is the phase B inverted, that is, leading phase A. The gain of the voltage equalizer amplifier 93 is initially set so that the phase B voltage output is equal to the phase A voltage output at the terminal at the highest frequency of adjustment of the oscillator, the output potential for the phase B branch now appearing at an output terminal |40 on the anode output circuit |35 across the anode coupling resistor indicated at |36.

The positive supply end of the resistor |36 is connected to a terminal |31 between the resistors |03 and |04 in the bleeder system. Thus the anode |38 receives a higher positive potential than the screen grid |02 for proper operation of the tube.

Therefore, at the anode end of the coupling resistor |36, or at the phase B terminal |40, the output voltage for phase B is caused to equal the output voltage for phase A at the output terminal and is leading because of the amplifier stage 93. Theseterminals are then coupled to separate amplifier stages in the now separated amplier or signal conveying channels forboth phases. At these points, namely, output terminals 88 and |40, vphase A and phase B may be individually considered, in effect, as single phase, so that the voltages at these two terminals, with respect to ground, although 90 degrees out of phase, are substantially separate, equal, singlephase, pure sine-wave voltages.

These voltages are necessarily inverted for push-pull operation of the polyphase thyratron inverter Ystages in a system ofpower supply in accordance with the invention, and the inversion may be accomplished by inverter amplifier Ytube means as inthe present Figure 2, or by means of coupling transformesr for converting from single phase to push-pull as in the circuit of Figure 3, as will be described hereinafter.

, In the present example, the phase-inverted voltage-gain stages 23 and 24 comprise two electronic amplifier' tubes |42 and |43, respectively, having control grids |44 and |45, coupled respectively to the input terminals 88 and |40 for phases A and B. Both amplier tubes are selfbiased as indicated by the cathode resistors |39 and |51, and the grid |44 is coupled to the terminal 88 through a suitable coupling capacitor |4|, while the terminal |40 is coupled to the grid |45 through a suitable coupling capacitor |46.

Both tubes |42 and |43 may be provided by two sections of a commercial type 6SN1 tube, and are operated with the cathodes above ground potential through the medium of coupling resistors |41 and |48, providing output coupling terminals |49 and |56, respectively, for the tubes |42 and |43. Likewise, in the anode circuits |5| and |52, output terminals |53 and |54, respectively, are provided with respect to output anode coupling resistors |55 and |56, thereby providing a well known form of phase inverter'amplifler tube circuit in each channel, to which output push-pull connections may be made in each case. Such a coupling arrangement is relatively simple, and by proper choice of resistors in the cathode and anode circuits, the output voltage at terminal |53 may be made equal to the output voltage at terminal |49, being 180 degrees out of phase, or push-pull, as are the voltages at the terminals |59 and |54 in channel or phaseB.

Furthermore, in accordance with the invention, the push-pull sine-wave voltages provided in each of the two-phase channels are now shaped for application to, and for most effective control of, full-wave thyratron inverter power circuits. The wave shaping is accomplished bymeans of the push-pull wave-Shaper amplifiers 25 and 26, referred to vin Figure l. These are provided in the present example by suitable electronic amplier tubes |58 and |59 in channel A, and |69 and |6| in channel B, together with proper control circuits. These tubes may likewise be provided by commercial double triodes of the 6SN1 type, one tube providing the triodes |58 and |59 in channel A, and the other tube providing the triodes |60 and |6| in channel B.

The input circuits of the tubes |58 and |59 are connected in push-pull relation across grid coupling resistors |62 and coupled to the terminals |53 and |49, respectively, of the preceding phase inverter amplifier |42, suitable coupling capacitors |63 being provided for each tube. A tap connection |65 between the resistors |62 is connected with a bias potential supply lead |66, which in turn is connected through a lter comprising a shunt capacitor |61 and series resistor |68, with a bias potential supply terminal |69 on a plate supply and bias circuit |10.

In a similarmanner, the tubes |60 and |6| are coupled across grid resistors |1| and |12 with the terminals |54 and |50, respectively, of the preceding phase inverter amplier |43, suitable coupling capacitors |13 being provided for each tube. It will be noted that the above described crossover coupling connections in phase B channel correct for the phase inversion in amplifier 93, in restoring phase B as the lagging phase.

A tap connection |14, between the resistors |1| 14 and |12, is connected through a bias supply lead |15 with the lead |66 and the filter IST-|68, whereby a predetermined negative biasing potential is applied to the tubes |58| 6| from the supply terminal |69 with respect to ground. It will be noted that the cathode leads |11 and |18 Vfor the push-pull connected tubes |58|59 `and |60|6| are connected to ground lead 35at the terminal indicated at |19.

The circuit arrangement for the bias supply, as will hereinafter be more fully described, provides for applying to the control grids |89 of the tubes |58--I 6 inclusive, with respect to the cathodes, a biasing potential such that the anode current of the tubes is reduced Well below cut-01T, thereby preventing the tubes from amplifying any signals below a predetermined minimum amplitude and serving to cut olf the peaks'and reduce the width of the sine input wave indicated by the voltage-wave curve diagram |8|, for producing. a corresponding pulse wave.

The output anodes ofthe tubes |59 and |59 are coupled through a push-pull output anode circuit |82|83 across a balanced-output impedance-coupling network comprising a balanced, or center-tapped, coupling inductor or inductance element |84 and output coupling capacitors |85 connected to output leads |81 and |88. The latter are connected through a suitable plug connector, indicated at |89, with terminals and |9| for a balanced, center-tapped output resistor means comprising resistor sections |92 and |93. The junction or tap connection on the resistor means, between the resistor sections |92 and 93, is provided by a terminal |94 connected through a lead |95 and the plug connector |89 to a bias supply lead |96 terminating at an adjustable contact |91 in the plate supply and bias circuit |18. This terminal is adjustable to provide a predetermined negative bias on the terminal 94 with respect to ground, for the control of the thyratron stage 1 representing the utilization circuit for the output of channel or phase A.

The output wave derived from the wave shaper amplifier stage |58| 59 through the output leads |81 and |86 will have a sharply peaked form,as indicated by the wave curvel99. This is determined by the anodepotential applied to the tube and the bias potential adjustment at the terminal |69. This is adjusted to reduce the anode current to a value below cut-off so that only'the peaks of the sine-wave input appear in the output as narrow pulses of less width than one-half the sine-wave form from which it is derived. The

lamplitude of the pulses is relatively high, be-

cycles and higher,l without reducing the useful tube life.

The channel or phase B output coupling connections are similar. The wave-Shaper amplier tubes |60 and |6| are provided with output anode circuits 200 and 20|, across which is connected an output coupling impedance comprising avcenter-tapped inductance element 202 and is provided with output coupling capacitors 203, thereby providing push-pull output connections for output leads 204 and 205 which extend through the output coupling plug connector |89 and connect with terminals 206 and for al pair of series-connected output coupling resistors 208 and 209 having a common or center-tap terminal 2|0 which is connected through a lead 21| with the lead |95, in the same manner as for the terminal |94.

With this arrangement, the exciter voltage output terminals |90 and |9| are connected in balanced or push-pull relation with the output anode circuits |82 and |83, respectively, for the wave-Shaper stage comprising the push-pull connected tubes |58 and |59, While the exciter voltage output terminals 205 and 201 are connected in balanced or push-pull relation with the output anode circuits 200 and 20|, respectively, for the wave-Shaper stage comprising the push-pull connected tubes |60 and IEI.

Thus there is provided, in connection with the oscillator, a two-phase or dual channel, pushpull output connection providing substantially equal push-pull voltages for control purposes, the control voltages being suitably amplified, peaked and reduced in width and adapted for controlling by pulses any utilization means such as the thyratron inverter stages 'I and 8 of the present example.

The thyratron inverter stages shown comprise a pair of push-pull thyratron inverters 2|5 and 2|6 in phase A, and 2|? and 2| in phase B, with grid circuits 220 and 22| connected through suitable series limiting resistors 2|?! with the terminals |90|9| and 20S-201, respectively, so that the resistors |92|93 and 20S- 209 form part of the grid circuit for the thyratrons and the grids are therefore biased negatively with respect to the cathodes, through the bias supply terminal I9? in the plate supply and bias circuit |0. lThis provides a separate bias potential source for the thyratron apart from the plate supply (not shown). The cathode supply circuit leads are indicated at 224, and one of the cathode connections is grounded, as indicated at 225, by means of an extension of the ground lead through the plug connector |89'.

The plate supply and bias circuit included in the exciter system may include the usual fullwave rectifier comprising an electronic rectier tube 230, connected to the plate supply secondary 23| of a power supply transformer 252, the primary 233 of which is energized from supply leads 234 provided with a connection through the plug connector |89 with power supply leads 235 in the thyratron power output unit. The center tap 23'! on the secondary 23| is connected through a lead 238 and a pair of potentiometer resistors 239 and 240 in parallel, with the ground lead 55, the return connection to the ground lead being made through a lead 242. This is the negative side of the supply.

The positive side of the plate supplyis taken from an output cathode terminal 243 and a supply lead 244 connected with the supply lead through a filter comprising a series lter resistor 245 and a shunt filter capacitor 245. Suitable lter capacitors 248 are provided in the plate supply circuit, and the bias supply arrangement is such that the bias supply terminals and |91 Yare relatively negative with respect to the ground lead by an amount determined by the tap connection. In the present example, 100 volts negative bias may be provided at the tap Wave-Shaper amplifiers 25 and 20, whereby transformer coupling may be used to obtain both the phase inversion from single-ended to push-pull, and a relatively high voltage gain for driving the push-pull Wave-Shaper amplifiers which follow in each phase or channel.

In addition, the circuit of Figure 3 provides means for applying to the thyratron circuit a separate series of positive voltage pulses for each thyratron control grid, and from which all of the negative pulses are eliminated. Thus in the two-phase system shown, the pulses applied to phase A are degrees in advance of the pulses applied to phase B and the tubes |53| S inclusive, are triggered at QO-degree intervals and in predetermined time phase relation to produce a series of output pulse waves that are applied to the thyratrons 2|5-'2|8, inclusive, Without the negative half waves.

The system for producing this result includes, in Figure 3, the phase inverter amplifier stages comprising the tubes |42 and |43 coupled, respectively, to the phase shift network and to the voltage equalizer amplifier as indicated. As hereinbefore stated, the phase-inverter amplifier tubes |42 and |43 are transformer-coupled to the push-pull wave shaper amplifiers |58-|6|, inclusive, through the medium of interstage push-pull coupling transformers 259 and 265. The transformer 260 ris provided with a centertapped balanced secondary 26|, the terminals of which are connected with the control grids 8@ of the wave shaper tubes |58 and |59 in phase A channel, While the transformer 265 is provided with a center-tapped balanced secondary 285, the

terminals of which are connected with the control grids 539 oi the wave-Shaper tubes |50 and |6| in phase B channel. The primaries 253 and 268 of the transformers 250 and 285, respectively, are connected in the respective anode circuits 210 and 21| ci the amplifier tubes 52 and |43. and both anode return circuits are connected with the positive supply lead 50.

The tubes |42 and |123 are self-biased through the usual cathode resistor means 213 andk 2M, provided with suitable bypass capacitors 215, and the control grids |44 and |45 are returned to the ground lead 35 through suitablergrid resistors 216. It will be understood that at the terminals 218 and 219, being input terminals for the grids |44 and H55, respectively, in the present example, the voltages supplied by the preceding portion of the excitorV system hereinbefore described are equal and 90 degrees out of phase.

The voltages applied to the grids |86 of the Wave-Shaper tubes IES-45|, inclusive, here shown as separate triodes, as may be desirable with cathode coupling, depend upon the voltage step-up ratios of the transformers 260 andv 265, which are made substantially equal and provide on the grids of ther tubes |58|6| relatively high t and'285l with a terminal 286, which "i's' biased negatively' with respect'toground by an amount equal to the bias required for the driven or excited thyratron inverter stage which follows,

' comprising the tubes 2|5 and 2|S in the present example. It will be noted that the grids 290 and 29| of the thyratron tubes 2|5 and '2|3 are coupled directly with the cathode terminals 238 and 289 through conductive circuit leads 292 and 293 and the series limiting resistors 2|9, thereby providing a direct cathode coupling output connection for the tubes |58|59 with the thyratron grids 290-29I through which a D.C. biasing potential may be applied to both of the latter grids.

For independently biasing the grids of the lwave-Shaper tubes |58-l59, it will further be noted that the center tap 295 on the secondary 26| is connected with the terminal 233 through a biasing resistor 296, shunted by a suitable bypass capacitor 291. The resistor 296 may have a value of 100,000 ohms, while the bypass capacitor may have a value of .5 mfd. for triode tubes shown, and likewise the resistors 284 and 285 in the cathode circuits may each have a value of 51,000 ohms in the system shown, being therefore of relatively low resistance and impedance for coupling over to the thyratron stages.

In a similar manner the cathodes 300 and 30| of the tubes |60 and IBI in phase B channel are connected through cathode resistors 302 and 303 with a center terminal 304, which in turn is connected with the center tap 305 of the push-pull :f secondary winding 236 of the input transformers 265'through a series biasing resistor 30'! shunted trol grids 3|5 and 3|6, respectively, of the thyratrons 2|? and 2|8 in the phase B power control circuit, series limiting resistors 2 I9 being included in each lead.

The terminal 304 is connected through a tieconnection lead 3|8 with the terminal 286 and is also connected through a lead 320 with a source of biasing potential (not shown) for applying thereto, with respect to ground 35, the maximum rated negative bias potential for the thyratrons 2|5-' 2| 8, inclusive, thereby to permit the minimum -deionization time in the operation of the thyratrous, for reasons which will hereinafter appear.

It will also be noted that the primary winding 263 of the transformer 255 is normally reversed `in its connection in the anode circuit 21! -to restore the phase B to a laggingrelation with respect to phase A, sincethe voltage equalizer arnplier, as hereinbefore noted, inverts, or changes by 180 degrees, the phase relation between the` two channels, which, however, has no effect upon the operation of the polyphase output power circuits controlled by the power supply system in any case. A double-pole, double-throw switch 322 may be introduced in the connections to the prim-ary winding to shift phase B as a convenient means of reversing the rotation of a motor in the power output circuit, as the switch may be light Y and inexpensive, since it handles negligible power.

It will further be noted that the anodes 3,25

elusive, are all connected with a common anode supply lead 323, which in turn is connectedat a terminal 321 with the positive potential'supply circuit 244. This for the reason that the output signal coupling is made in connection with the cathode circuits, as previously described.

It will also be noted that, in showing the connections between the push-pull wave-Shaper amplifiers and the thyratron inverter stages, the connector plug arrangement has been omitted for the purpose of simplifying the drawing and for aiding in an understanding of the operation of the circuit, although it should be understood that some form of plug connection may normally be made between the exciter system and the utilization circuit, represented by the thyratron inverter, as in the case of Figure 2.

Between the leads 292 and 293 for phase A, -and between the leads 3|3 and 3|4 for phase B, representing the output circuits of the two phases, is shown a pulse-wave time relation diagram or graph indicating thel voltage pulses in their time.. phase relation as they appear on the output leads and as they are applied to the thyratrons. As indicated, a sharp positive pulse 330 is applied to the lead 292 and the thyratron grid 290, followed on the next quarter-period, by a similarsharp positive pulse 33| in phase or channel B, through the output lead 3|3, and being applied to the grid 3|5. This is followed after 90 electrical degrees, or on the next quarter-period, by a sharp positive pulse332 through the output lead 293, and this is applied to the grid 29|, and 90A degrees, or a quarter-period later, a similar pulse` 333 is applied to the grid 3|6 through the loutput lead 3M, whereupon the cycle repeats as indicated by the pulse wavey 334,whichis applied to the grid 290 through the outputA lead 292 electrical degrees later. 7

From the foregoing description it will be seen that the thyratrons are pulsed alternately in each phase, degrees apart, in the normal pushpull relation and that the pulses in phase B lag the pulses in phase A by 90 electrical degrees or one-quarter period, thereby producing in the output circuits of the thyratrons (not shown) a twophase output power supply controlled in frequency by the exciter system of the presentY invention. K

The circuit 'of Figure 3 has not only the advantage that transformer coupling may be used, but also, as indicated by the pulse wave diagram, only positive pulses are applied to the thyratrons, since negative pulses are suppressed by reason of the direct connection to the cathodes-of the push-pull wave-Shaper ampliers, Aand because the wave-Shaper amplifiers are operated below cut-off by means of the grid current bias provided by the resistors 296 and 30?, so that only the peaks of the sine-wave input wave |8| appear in the output circuit, the negative half waves being eliminated. This latter feature permits the maximum rated negative bias to be applied continuously to the thyratron inverter tubes, which is not the case when the negative half waves are present as in the circuit of Figure 2. Therefore, the thyratron triggering or eX- citer system embodying the modification of Figure 3 provides the possibility of operating the thyratrons at relatively high frequencies, because the deionization time is reduced to a minimum by the presence of the maximum negative biasand this may be done without danger of reducingfthe tube life through malfunctioning or improper grid p trial applications.

19 loading, or excessive bombardment of the grid by positive ions..

The use of transformer coupling into the pushpullwave-Shaper amplifier' isv permissible in the high frequency control. system of the present invention, for the reason that the voltage wave at that point is still a sine-wave, for which an inexpensive transformer may be designed to provide` coupling without distortion.

The use of transformers for coupling into a push-pull wave-Shaper amplifier may be desirable, a's the number' of tubes is reduced. In some instancesl the use of phase-inverter electronic amplifier tube stages may be desirable, Where the push-pull balance, or gain, is to be adjusted slightly after the apparatus is in. use, for the reason` that avrather high voltage is required to operate the class C stages in the wave shaper amplifiers, since they are biased well beyond anode current cut-01T to produce the narrow peaked pulses for triggering the thyratron power stages which follow.

In this connection, it may be noted that an impcd-ance coupling network is used in the output circuit of each of the push-pull wave-Shaper amplifiers, rather than transformer coupling, because at this point the wave is no longer a sine wave, but is a peaked-f, sh-arp pulse, and therefore low wave distortionv is provided at all frequencies. Furthermore, positive pulses without negative pulses, as produced in the circuit of Fgure; 3,. cannot be transmitted through a transformer. If! transformers are used in that output coupling of Figure 2, it has been found that sharp excitation. of the transformer secondary may produce indeterminate transient voltages after the quenching point in. the operating-cycle of each of. the; thyratrons which follow in the power stages. Furthermore, the impedance coupling output or grid resistors {B2-|93 and. 208-2018 provide a critical damping load on the coupling reactors or impedances [84 and- 202 so that substantially a constant high impedance is provided in the output anode circuits of the wave-Shaper amplifier tubes ISS-|61 inclusive.

On the other hand, if the wave-shaping were accomplished at another point in the system prior to the phase division,y such as at the oscillator itself or at the buffer amplifier, for example, it would not be possible to obtain identical wave shapes with varying frequency from the output of the two-phase or phase-shift network 2l if the input wave were a complexV wave, as it would be under the conditions above stated. It is for the same reason that a substantially clean and perfect sine wave is providedv at the phase-shift network for better phase splitting or phase shifting results.` This, of course, includes the use of the low pass filter in the outputr of the oscillator, as Well as stabilizing the limiting oscillator voltages as has hereinbefore been described.

Accordingly, it will be seen that it is desirable that the shaping of the sine wave into sharp pulse form follow the phase splitting or shifting in the ltwo-phase network, and that for proper wave shaping relatively high voltage gain is required preceding the shaping and that this, in turn, is followed by substantially constant high impedance coupling networks for low distortion of the shaped pulse wave in its application to the utilization circuit, which generally is the thyratron inverter power handling stage of a complete power supply system for the control of high frequencyalternating current motors and the like in indus- For such control it is further 2f) desirable to provide a seriesv of positive pulses while causing negative pulses to be suppressed.

Referring now to the drawings, the operation of the system is asv follows: The electron. tube oscillator, amplifiers and rectiers' are energized by means of the plate supply and bias circuit when connected with suitable alternating current through the supply leads 234 and 235. The oscillatorv range control knob 'I1 is adjusted to establish the desired frequency range of operation, and the frequency control knob 18 is set for the desired speed in that range.

The oscillator then applies to the buffer' ampliner 58V a sine-wave voltage at the frequency selected, and suitably limited and free of liarmonics, and the amplifier, in. turn, delivers the sine-wave voltage to the phase shift network 2l, where it is split ordivided into two corresponding phase A and B voltages, the BV phase voltage being further equalized by the voltageequalizer amplifier 22, so that either through the .transformer coupling of Figure 3, or` the electron tube coupling of Figure 2, balanced push-pull high voltage in sine-wave form is delivered to the grids lilA of the two pairs of push-pull waveshaper amplifiers in each of the phase A and phase B controlling and amplifying channels. The sine wave, as indicated at IBI- in Figure 2, is then changed to a similar wave at the same frequency which is sharply peaked and reduced in Width for application to the output terminals i-[2| and 23E-2M, through the push-pull impedance coupling networks2'l-28 and the utilization means which, in the present example, is indicated as thyratrori power inverters, to which the invention is particularly adapted.

The pulsed. output waves in two-phase. pushpull relation may be applied to any suitable. utilization means, and in particu-lar to the control grids of balanced push-pull thyratron inverters, as shown in Figure 2, for control of a two-phase motor as outlined in Figure l. Similar arrangements may be provided for other polyphase circuits in which the sinusoidal wave is subsequently modified to the pulse shape as described, although the two-phase method of generating the voltage is at present preferred.

A variable frequency control system, in accordance with the present invention, is therefore adapted for the control of any pulse-operated system, such as high-frequency thyratron inverter for high speed induction motor operation, and provides an improved electronic means for producing full-wave, two-phase voltages of variable frequency which is highly stabilized and adapted for this purpose. In connection with a polyphase and full-wave thyratron inverter system 'for the control of polyphase power, it provides a simplied and flexible substitute for known rotary power supply devices such as motor generators, dynamotors, and the like, in speed ranges above safe or practical limits for the operation of such devices.

I claim:

l. An exciter system for thyratron power inverters and the like, comprising in combination, a controlled frequency sine-wave voltage supply circuit, a phase-shift network coupled to said circuit providing two voltages of differing phase in response to an applied voltage from said source, one Vof said voltages being variable with frequency, equalizer amplifier means coupled to said network for deriving substantially a constant voltage output from said variable voltage and of equal amplitude with the other of said voltages, a

pair of thyratron inverters, and separate channel circuit means coupled with said network and equalizer amplifier means for applying said equalized yoltages to said inverters in predetermined time-phase relation.

2. An exciter system for thyratron power inverters and the like, as defined in claim l, wherein each of said separate channel coupling circuit means includes a wave-Shaper circuit for transforming the sine-wave voltages into spaced voltage pulses of predetermined polarity and amplitude.

3. An exciter system for thyratron power inverters and the like, as defined in claim 2, wherein the wave-Shaper circuits provide only positive voltage pulses of relatively high amplitude, and wherein a bias potential supply circuit is provided to apply to each of the thyratron inverters a negative biasing potential of the order of the rated maximum therefor, whereby relatively high frequency operation may be attained.

4. An exciter system for thyratron power inverters and the like, comprising in combination, an electronic oscillator operable at a predetermined freqeuncy, phase-shifting voltage-divider means coupled with said oscillator for deriving therefrom a two-phase output voltage, electronic tube amplifier means providing separate channel amplification of said two-phase voltageand being biased to provide corresponding voltage pulses of less than one-half cycle duration, and

l an output impedance coupling circuit lfor Ysaid amplifier means adapted to apply said pulses" to said inverters in predetermined time-phase relation.

5. An exciter system for thyratron powery inverters and the like, as defined in claim 4, wherein the oscillator is provided withfrequency determining control circuits, and wherein thel electronic tube amplifier means in each channelina tuned electronic-tube oscillator circuit adapted to provide substantially a sine-wave output voltage, a frequency control network in said oscil- ,lator circuit, a phase-shift network coupled to said circuit for dividing the oscillator output voltage into corresponding voltages of differing `phase and providing differing output circuits therefor, phase-inversion means coupledto each of said output circuits for developing substantially equal push-pull voltages for each phase of relatively high amplitude, a push-pull electronic tube wave-Shaper amplifier coupled to said last- -named phase-inversion means for each phase, -means for operating each of said wave-Shaper amplifiers below anode current cut-off, and a push-pull impedance coupling network for each ofsaid wave-Shaper amplifiers providing-a `plurality of balanced output circuits for said system for the operation of controlled thyratron iil verter utilization means.

'7. An electronic high frequency thyratron inverter control system as defined in claim 6, wherein the phase-shift network comprisesv a bridge circuit having substantially equal ratios of resistance and reactance oppositely connected in each arm tending to produce a voltage output for one phase which varies inversely with frequency, and wherein a voltage equalizer amplifier circuit is interposed between an output circuit therefor and the phase-inversion means for said output circuit.

8. An electronic high frequency control system as defined in claim 6, wherein a voltage equalizer amplifier circuit is interposed between the phaseshift network and the phase-inversion means for one output circuit of said phase-shift network, and wherein the output circuits for each waveshaper amplifier are cathode coupled, thereby to produce positive pulses to the exclusion of negative pulses for the high frequency excitation of said thyratron inverters and the like, and means for imparting a high negative bias to said output circuits which is of the order of the rated maximum for such thyratron inverters.

9. An electronic high frequency control system as defined in claim 6, wherein a voltage equalizer amplifier circuit is interposed between the phaseshift network and the phase-inversion means for one output circuit of said phase-shift network, said last-named amplifier circuit being responsive to the output voltage of said one output circuit and including a gated rectifier and a bias voltage output circuit therefor, whereby the gain is controlled, and wherein the output circuits for each wave-Shaper amplifier are cathode coupled, thereby to produce positive pulses to the exclusion of negative pulses for the high frequency excitation of said thyratron inverters and the like, and vmeans for imparting a high negative bias to said output circuits which is of the order of the rated maximum for such thyratron inverters, said last-named means including an operating voltage supply circuit for said system and a bias potential source therein connected with said Output circuits. f

10. An exciter system as defined in claim 6 wherein each of said wave-Shaper amplifiers is provided with transformer coupled push-pull input circuits as part of said phase-inversion means and with a reversible primary connection in one transformer coupled input circuit for effecting a reversal of the phasing of said output voltages from the phase-shift network.

11. A high frequency'power supply system for polyphase alternating current motors and the like, comprising a full-wave thyratron inverter adapted to be coupled with each phase thereof for applying alternating current power thereto, a power output coupling network for each inverter, a sine-wave oscillator coupled to each of said fullwave thyratron inverters for applying excitation voltage thereto in predetermined phase relation one with respect to the other, said oscillator having an adjustable frequency control network and a common control element for simultaneously adjusting the frequency of the oscillator and the y output coupling network of each thyratron inverter whereby the operating speed of the motor may be adjusted, circuit means for stabilizing and limiting the oscillator output voltage, a phase-shift network coupled to the oscillator for separating the oscillator output voltage into two components differing in phase, electronic tube amplifier means providing separatev channel amplification and control in the coupling between the oscillator and said inverters for separately exciting each of said inverters, and including a pair of electronic amplifier tubes biased beyond anode current cut-off for imparting a peaked pulse shape tothe oscillator voltage wave,thereby yto improve v.the iexcitationaction on lsaid thyra tron inverters.

.12. The combination as :defined in claim ll,

wherein each full-wave thyratron inverter is biased negatively to substantially maximum rated voltage, vthereby to provide maximum deicnization yaction in response to excitation at relatively high frequencies, and wherein the wave-Shaper ampliers in each phase are further cathodecoupled directly to the thyratron inverters, thereby to eliminate the negative half waves of each voltage pulse and to apply to said thyratron inverters only positive'half -wave pulses and further toimprove the eiciency of operation at said high frequencies.

13. A high frequency triggering pulse generator system for polyphase thyratron power inverters adapted for operation of high speed industrial motors and the like, comprising in combination,

a sine-wave source of triggering potential having frequency control means for determining the output frequency, electronic amplifier and circuit means for modifying the sine-wave triggering potential intwo separate amplifying channels to provide two corresponding triggering potentials of peaker wave form of the same frequency and to the exclusion of negative half wave peaks, a

pair of vcathode-coupled output circuits for each amplifying channel providing direct thyratron grid circuit connections, and bias potential supply connections through said output circuits for applying relatively high negative biasing potentials to said grid circuit con ections of the order of the rated maximum for said inverters, whereby improved operation of said inverters atrelatively high frequencies is attained.

vla. In a high frequency alternating current power supply system, the combination with a pair of full-wave thyratron power inverters, of

variable frequency excitation means therefor,

comprising a tunable stabilized electronic tube oscillator for generating substantially Vconstantamplitude output voltages at dii-ferent frequencies, a phase-shift network providing dual channel output circuits coupled to the oscillator, variable gain signal-amplitude-responsive ampliiier means for equalizing the output voltage in said output circuits with change in frequency, a pushpull connected class C amplifier coupled with each of said output circuits for peaking the output voltage waves to provide corresponding pulse waves in predetermined time-phase relation, and impedance lcoupling means providing an output connection between each cla-ss C amplifier and one of the thyratron power inverters for applying said pulse waves thereto at the oscillator' frequency.

V15. In a high frequency alternating current power supply system, the combination as in claim le, wherein the phase-shift network comprises a bridge circuit having substantially equal ratios of resistance and reactance oppositely connected in each arm, and wherein means are provided for applying a high negative bias through said output connection to sai-d thyratron power inverters which is of the order of the rated maximum for such thyratron' inverters.

' 16. An exciter system for thyratron power inverters and the like, comprising in combination, an electronic oscillator operable at a predetermined frequency and having an output circuit, phase-shifting voltage-divider means coupled with said oscillator output circuit for deriving therefrom a two-phase output voltage, electronic tube amplifier means Aproviding separate channel amplification Vof 'said "two-phase' voltage and :be-

ing biased to provide corresponding voltage pulses of less than one-half-cycle duration, 'and an output impedance coupling circuit for said amplifier means adapted to apply said pulses to said Y inverters in predetermined time-phase relation,

and said phase-shifting rvoltage-divider means comprising ra bridge circuit having substantially equal ratios of resistance and reactance oppositely connected in each of two parallel branches across the oscillator output circuit, one branch including a resistance element and a reactance element in series in the order named, and the other branch including a reactance element and a resistance element in series in the order named, with output terminals interposed in each branch between the resistance and the reactance elements.

17. An exciter system for thyratron power inverters and the like, comprising in combination, a sine-wave voltage supply circuit, tuning means for determining the frequency of said circuit, a single phase sine-wave voltage output circuit including a high potential lead and a common ground return lead for the system coupled to said voltage supply circuit, a phase-shift network comprising two parallel branch circuits connected between said leads providing substantially equal ratios of resistance to reactance, one branch circuit comprising series cormected resistance and reactance elements in the order named and the other branch circuit including series connected reactance and resistance elements in the order named, dualchannel output circuit means for deriving an output Voltage across'the reactance element of one branch and the resistance'element of the other branch and including in each channel of said output circuit means a pair of push-pull coupled electronic tube amplifiers biased and controlled for imparting a peaked pulse shape to said voltages for improved thyratron inverter excitation, and means providing an impedance coupling output connection for each of said pulse-shaping ampliiiers adapted for coupling each with a pair of balanced thyratron inverters, whereby two-phase power may be rderived therefrom.

18. An exciter system for thyratron power inverter and high frequency motor control, comprising in combination, a variable frequency tunable sine-wave oscillator having a main tuning inductance, a frequency control network connected in parallel with said tuning inductance, a gated rectifier and series limiting resistor connected effectively in parallel with said tuning inductance, means for stabilizing the 0peration of said oscillator including a series limiting impedance in the anode circuit thereof and acathode bias resistor, an output circuit for said oscillator including a low pass lter for frequencies `below the maximum frequency to which said oscillator is tunable, a phase-shift network coupled to said oscillator output circuit for receiving the sine-wave output therefrom and comprising a pair of parallel branch reactance-resistance circuits, each having an output connection thereon for dividing the oscillator vsine-waveY output voltage into two sine-wave voltages of differing phase, means for amplifying and transforming each of said sine-wave output voltages into balanced push-pull voltages of predetermined amplitude, and means for modifying each of said balanced push-pull sinewave voltages to `provide corresponding peaked exciting pulses at the same frequency, a pluoperation of said oscillator for the production of power corresponding thereto in frequency.

19. An exciter system for thyratron power inverters and the like, comprising in combination, a pair of exciter voltage amplifying channels, high frequency alternating current exciter voltage supply means coupled to said amplifying channelsin parallel and including controlling networks for maintaining thereon sine-wave exciter voltages of differing phase and of substantially constant amplitude, phase-inverter electronic amplier stages in each of said channels, a wave-Shaper circuit coupled to each phase-inverter stage, said wave-Shaper circuits each including a pair of push-pull connected electronic amplifier tubes operating beyond anode cut-off for transforming said sine-wave exciter voltages into spaced, substantially sharp voltage pulses of predetermined polarity and amplitude, an impedance-coupled output` network for each of said wave-Shaper circuits, and a balanced thyratron inverter coupled to each of said impedance coupled networks to receive voltage pulses therefrom in predetermined timephase relation for the generation of alternating current power at predetermined high frequencies.

20. In combination, a tunable oscillator, a frequency determining circuit for said oscillator, amplitude and feedback stabilizing circuits for said oscillator operative to produce substantially a sine-wave output voltage therefrom of predetermined amplitude, a phase-shift network coupled to said oscillator having resistance and reactance means connected in separate output channels for providing output voltages corresponding to the oscillator output voltage in differing; phase relation, a low-pass filter circuit interposed between said phase-shift network and the oscillator having a cut-off frequency above the operating frequency of the oscillator, phase inverter circuit means coupled to the output circuits of said phase-shift network for converting the single phase output in each channel to push-pull positive and negative voltage waves, a balanced wave-Shaper electronic amplifier coupled with each phase inverter means and biased to provide pulse waves of substantially.

less than one-half wave duration and of a predetermined high amplitude, a full-wave thyratron power inverter comprising a pair of balanced inverter tubes having control grids impedancecoupled in push-pull relation to each of said lastnamed amplifiers, and means for applying a biasing potential to said thyratron inverters through said coupling networks.

21. An exciter system for thyratron power inverter and high frequency motor control, comprising in combination, a variable frequency sinewave voltage source, a p-hase-shift network coupled to said source for receiving the sine-wave output therefrom and comprising a pair` of paralf lel branch reactance-resistance circuits, each of said circuits having an output connection thereon for dividing the sine-wave output voltage into two sine-wave voltages of differing phase, electronic tube amplifier means for transforming each of said sine-wave output voltages into push-pull voltages of predetermined amplitude, additional electronic tube amplifier means for modifying each of said push-pull sine-wave voltages to provide corresponding exciting pulses at the same frequency, and impedance coupling output networks'for said amplifier means adapted for coupling with the control grid circuits of two fullwave thyratron inverters or the like, whereby alternating current power may be provided at the frequency of said sine-wave source.

22. An exciter system for thyratron power inverter and high frequency motor control, comprising in combination, a variable frequency sinewave voltage source, a phase-shift network coupled to said source for receiving the sine-Wave output therefrom and comprising a pair of parallel branch reactance-resistance circuits, each of said circuits having an output connection thereon for dividing the sine-wave output voltage into two sine-wave voltages of differing phase, electronic tube amplifier means for transforming each of said sine-wave output voltages into push-pull voltages of predtermined amplitude, additional electronic tube amplifier means for modifying each of said push-pull sine-wave voltages to provide corresponding exciting pulses at the same frequency, a plurality of full-wave thyratron inverter power controlling circuits including two pairs of push-p ull input grid circuits therefor, and impedance coupling networks for applying each of said exiciting pulses to each pair of said grid circuits in balanced relation, thereby to control said thyratron inverter circuits at the frequency of said sine-wave voltage source for the production of alternating current power corresponding thereto in frequency.

GALAN W. DEMUTH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,934,400 Bollman Nov. 17, 1933 2,117,587 Young May 17, 1938 2,385,641 Peterson Sept. 25, 1945 2,404,344 Wild July 16, 1946 2,446,607 Peterson Aug. 10, 1948 

